The patch titled
md: improve the is_mddev_idle test
has been added to the -mm tree. Its filename is
md-improve-the-is_mddev_idle-test.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: md: improve the is_mddev_idle test
From: NeilBrown <neilb@xxxxxxx>
During a 'resync' or similar activity, md checks if the devices in the
array are otherwise active and winds back resync activity when they are.
This test in done in is_mddev_idle, and it is somewhat fragile - it
sometimes thinks there is non-sync io when there isn't.
The test compares the total sectors of io (disk_stat_read) with the sectors
of resync io (disk->sync_io). This has problems because total sectors gets
updated when a request completes, while resync io gets updated when the
request is submitted. The time difference can cause large differenced
between the two which do not actually imply non-resync activity. The test
currently allows for some fuzz (+/- 4096) but there are some cases when it
is not enough.
The test currently looks for any (non-fuzz) difference, either positive or
negative. This clearly is not needed. Any non-sync activity will cause
the total sectors to grow faster than the sync_io count (never slower) so
we only need to look for a positive differences.
If we do this then the amount of in-flight sync io will never cause the
appearance of non-sync IO. Once enough non-sync IO to worry about starts
happening, resync will be slowed down and the measurements will thus be
more precise (as there is less in-flight) and control of resync will still
be suitably responsive.
Signed-off-by: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/md/md.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN drivers/md/md.c~md-improve-the-is_mddev_idle-test drivers/md/md.c
--- a/drivers/md/md.c~md-improve-the-is_mddev_idle-test
+++ a/drivers/md/md.c
@@ -5105,7 +5105,7 @@ static int is_mddev_idle(mddev_t *mddev)
*
* Note: the following is an unsigned comparison.
*/
- if ((curr_events - rdev->last_events + 4096) > 8192) {
+ if ((long)curr_events - (long)rdev->last_events > 4096) {
rdev->last_events = curr_events;
idle = 0;
}
_
Patches currently in -mm which might be from neilb@xxxxxxx are
origin.patch
revert-md-improve-partition-detection-in-md-array.patch
md-avoid-a-possibility-that-a-read-error-can-wrongly-propagate-through-md-raid1-to-a-filesystem.patch
nlmclnt_recovery-dont-use-clone_sighand.patch
git-md-accel.patch
freezer-add-try_to_freeze-calls-to-all-kernel-threads.patch
introduce-freezer-flags-rev-2.patch
md-improve-the-is_mddev_idle-test.patch
use-menuconfig-objects-ii-md.patch
md-dm-reduce-stack-usage-with-stacked-block-devices.patch
-
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